Nonlinear optical potassium niobate nanocrystals as harmonic markers: the role of precursors and stoichiometry in hydrothermal synthesis

Abstract

Nanocrystals of alkaline niobates are currently being discussed for various applications because of their diverse and remarkable properties. Although the growth of bulk niobate crystals is well established, little is known about respective nanocrystals and the optical properties of niobates below 100 nm. A systematic view of the hydrothermal synthesis of potassium niobate with respect to the precursor species reveals the sensitive dependence of the resulting crystalline phases and sizes on the educt modifications. With a variation of stoichiometry of the procedure, the product modification and crystallite size can be changed. By means of second harmonic generation, nanocrystalline potassium niobate offers the possibility for use as an optical marker in high resolution nonlinear microscopy. Redispersed particles show a significant second harmonic generation signal throughout the visible spectral range.

Remarkable Infrared Nonlinear Optical, Dielectric, and Strong Diamagnetic Characteristics of Semiconducting K3[BiS3]

“…In the case of 1 , the calculated f R (1500 nm) is 3 × 10 7 . This value is comparable with the values obtained for LiNbO 3 , KNbO 3 , and NaNbO 3 , which are known to be the reference materials in nonlinear optics because of their high nonlinear optical coefficients.…”

Absorption and Remission Characterization of Pure, Dielectric (Nano-)Powders Using Diffuse Reflectance Spectroscopy: An End-To-End Instruction

“…DR) against the photon energy hν, the band gap energy E g can be extracted by a linear fit at its rise as shown in Figure 12. The crossing point between fit and abscissa will then immediately yield E g [41,[111][112][113]. This procedure is also known as Tauc plot and is a powerful tool in the field of quantitative determination of band gaps and absorption centers.…”

Solution‐Based Synthesis Routes for the Preparation of Noncentrosymmetric 0‐D Oxide Nanocrystals with Perovskite and Nonperovskite Structures

“…Similar intermediates were also recently evidenced when different niobium oxides are solvothermally treated to produce KNbO 3 nanocrystals of the orthorhombic form in KOH solutions. [ 116 ] Note that for the nonperovskite LiNbO 3 crystalline structure, a similar aqueous route is unsuccessful since the rock‐salt Li 3 NbO 4 structure is typically obtained with another nonidentified hydrous phase according to the initial Li content. [ 117 ] In that latter case, the prerequisite of a homogeneous dispersion of the metal precursors at the atomic scale from the Nb‐rich hexaniobate species that do not decompose into monomeric [NbO 6 ] 7− ions might explain why the formation of the functional LiNbO 3 phase is prevented.…”

“…[ 114 ] Similarly, the orthorhombic and monoclinic forms of KNbO 3 were prepared after simply changing the niobium precursor from several crystallized and amorphous Nb 2 O 5 powders and from niobium oxalate and NbCl 5 . [ 116 ] When the Amm2 phase is obtained, the excitation tunability of the SHG response of colloidal suspensions of KNbO 3 nanocrystals was also demonstrated. As already pointed out, the absence of local stoichiometry in the precursors can severely complicate the exact derivation of a crystallization mechanism without an extensive use of sophisticated in situ time‐ and temperature‐resolved experiments.…”